Among integrated circuit (IC) fabrication techniques, a photolithography process is an important technique used in forming selected circuit patterns on a substrate such as a semiconductor wafer. As integration density of IC is increasing in fabricating smaller and more complex circuits of semiconductor devices, advanced lithography techniques are accordingly required in producing smaller critical dimensions (CDs) and fine patterns.
During the photolithography process of producing a semiconductor device, light energy is applied (i.e. an exposure process) through a photomask (also referred to as a reticle) onto a photoresist material previously formed on a wafer, in order to define circuit patterns which will be etched in a subsequent process. The photomask is required to remain clean and without damage during the exposure process. However, electrostatic discharge (ESD) is likely to occur during the exposure process, and results in discharge of small current between two isolated portions of a conductive pattern (that is generally metallic, such as a light-shielding layer) on the photomask, which may melt a circuit line and destroy the circuit pattern. The small current may result from movement of electrons and electron holes coming from a photoelectric effect during the exposure process, for example, when argon fluoride (ArF) excimer laser having a wavelength of 193 nm is applied as the light energy. Damages to the circuit line and/or the circuit pattern results in defects of the produced semiconductor device.